1. Field of the Invention
The present invention relates to a mechanical safety device for an injection molding machine.
2. Description of the Related Art
According to a known technique, an injection molding machine in which a stationary platen and a pressure-receiving platen are connected by tie-bars, which penetrate a movable platen for movement between the stationary platen and the pressure-receiving platen, is provided with a safety device. The safety device comprises a laterally openable safety door on the flank of a mold opening/closing portion between the movable platen and the stationary platen. If the safety door is opened, a stopper engages with engaging step portions of a rod, which spans between the movable and stationary platens or between the movable platen and the pressure-receiving platen, in an associated manner, thereby preventing movement of the movable platen.
FIG. 7 is a view illustrating a first example of a mechanical safety device attached to a prior art injection molding machine.
The injection molding machine comprises a movable platen 1, stationary platen 3, and pressure-receiving platen 4 on a base 17, and the stationary platen 3 and the pressure-receiving platen 4 are connected by tie-bars 18, which penetrate the movable platen 1. Guided by the tie-bars 18, the movable platen 1 is movable toward or away from the stationary platen 3. The mechanical safety device used in the injection molding machine comprises a rod 2, formed with engaging step portions and tapered surfaces arranged alternately, and a ratchet 5 capable of engaging with the engaging step portions of the rod 2. One end of the rod 2 is secured to the movable platen 1, the other end is directed horizontally toward the stationary platen 3, and the ratchet 5 on the stationary platen 3 is engageable with the engaging step portions of the rod 2. Alternatively, one end of the rod 2 is secured to the movable platen 1, the other end is directed horizontally toward the pressure-receiving platen 4, and the ratchet 5 on the pressure-receiving platen 4 is engageable with the engaging step portions of the rod 2.
In the case where the rod 2 is secured to the movable platen 1 so as to be directed toward the stationary platen 3, however, it may project forward if the mold is thin. Therefore, a separate cover 6a needs to be provided lest an operator hit the rod 2, so that the working efficiency is reduced, and an increase in costs is entailed. In the case where the rod 2 is secured to the movable platen 1 so as to be directed toward the pressure-receiving platen 4, on the other hand, it may project rearward. Therefore, the rod 2 needs to be located so as not to interfere with components mounted on the pressure-receiving platen 4, so that its place of installation is restricted. If the mold is thick, moreover, a rear cover 6b should be enlarged lest the rod 2 project from the machine.
FIGS. 8 and 9 are views illustrating a second example of a safety device of a mold clamping mechanism of the prior art injection molding machine. This technique is disclosed in Japanese Patent Application Laid-Open No. 10-113971.
As shown in FIG. 8, a rod 2 has its rear end secured to the flank of a movable platen 1 and its distal end portion directed horizontally toward the flank of a pressure-receiving platen 4. The distal end portion of the rod 2 is formed with a required number of engaging step portions and tapered surfaces alternately arranged at regular intervals. A safety door 7 is horizontally movable guided by a guide frame 8, and it serves to open or close the flank of a mold opening/closing portion between the movable platen 1 and a stationary platen 3.
A seat plate 9 is secured to the guide frame 8, two link arms 10 are rotatably mounted on the seat plate 9, and a link bar 11 is connected between the respective distal ends of the link arms 10. When the link arms 10 and the link bar 11 are in positions indicated by full lines in FIG. 8, the safety door 7 is open. Since a lever member 12 is lowered in this state, as indicated by full line in FIG. 9, a ratchet 5 pivots clockwise as in FIG. 9 and engages with the engaging step portions of the rod 2. Thus, movement of the movable platen 1 is prevented. If the safety door 7 is closed, on the other hand, the link arms 10 and the link bar 11 are displaced (or the link bar 11 ascends) as indicated by two-dot chain lines in FIG. 8 as the door 7 moves in its closing direction. As the link bar 11 ascends, the lever member 12 pivots counterclockwise (or upward), as indicated by two-dot chain line in FIG. 9. Thereupon, the ratchet 5 is disengaged from the engaging step portions of the rod 2, as indicated by two-dot chain line in FIG. 9, so that the movement of the movable platen 1 ceases to be prevented.
In the device described in Japanese Patent Application Laid-Open No. 10-113971 mentioned above, it is necessary to secure the seat plate 9 to the guide frame 8 and locate the link bar 11 and the rod 2 under the guide frame 8, so that a vertically wide installation space is needed beside the mold clamping mechanism. Therefore, the interior of the machine cannot be easily accessed during maintenance work. As the downward distance from the guide frame 8 to the rod 2 increases, the seat plate 9 or the link arms 10 are enlarged, so that the maintenance efficiency worsens and the costs increase.
FIG. 10 is a view illustrating a third example of a safety device of a mold clamping mechanism of the prior art injection molding machine. This technique is disclosed in Japanese Utility Model Application Laid-Open No. 58-112518.
One end of a serrated rod 2, which is formed with engaging step portions and tapered surfaces arranged alternately, is secured to a stationary platen 3. The other end of the rod 2 is directed horizontally toward a movable platen 1. The movable platen 1 is provided with a cylinder 14, which contains the ratchet 5 for advance and retreat. The movement of the movable platen 1 can be prevented by operating a wire in a power transmission tube 15, whose distal end is connected to the ratchet 5 in the cylinder 14, to cause the ratchet 5 to project from the cylinder 14 and engage with the engaging step portions of the rod 2.
In the device described in Japanese Utility Model Application Laid-Open No. 58-112518 mentioned above, the sliding resistance of the wire in the power transmission tube 15 due to friction may become too high for the safety device to operate when the tube 15 is bent. Since the end of the power transmission tube 15 advances or retreats together with the movable platen 1, moreover, a mechanism is needed to hold the power transmission tube 15 lest it interfere with a toggle mechanism (not shown) or the door, depending on the variable degree of bending of the power transmission tube 15.